Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write, but other information storage devices also include heads—sometimes including heads that cannot write. For convenience, all heads that can read are referred to as “read heads” herein, regardless of other devices and functions the read head may also perform (e.g., writing, flying height control, touch down detection, lapping control, etc.).
In a modern magnetic hard disk drive device, each read head is a sub-component of a head gimbal assembly (HGA). The read head typically includes a slider, and a read/write transducer deposited on a trailing end of the slider. The read/write transducer typically comprises a magneto-resistive read element (e.g., so-called giant magneto-resistive read element, or a tunneling magneto-resistive read element), and an inductive write structure comprising a flat coil deposited by photolithography, and a yoke structure having pole tips that face a disk media.
The HGA typically also includes a suspension assembly that includes a mounting plate, a load beam, and a laminated flexure to carry the electrical signals to and from the read head. The read head is typically bonded to a tongue feature of the laminated flexure. The HGA, in turn, is a sub-component of a head stack assembly (HSA). The HSA typically includes a rotary actuator having a plurality of actuator arms, a plurality of HGAs (attached to the actuator arms), and a flexible printed circuit that includes a flex cable. The mounting plate of each suspension assembly is attached to an arm of the rotary actuator (e.g., by swaging), and each of the laminated flexures includes a flexure tail that is electrically connected to the HSA's flex cable (e.g., by solder reflow bonding or ultrasonic bonding).
Modern laminated flexures typically include electrically conductive copper traces that are isolated from a stainless steel support layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flex cable on the actuator body, each HGA flexure includes a flexure tail that extends away from the head along the actuator arm and ultimately attaches to the flex cable adjacent the actuator body. That is, the flexure includes electrically conductive traces that are electrically connected to a plurality of electrically conductive bonding pads on the head (e.g., by 90° solder jet bonding), and extend from adjacent the head to terminate at electrical connection points at the flexure tail.
The position of the HSA relative to the spinning disks in a disk drive, and therefore the position of the read heads relative to data tracks on the disks, is actively controlled by the rotary actuator which is typically driven by a voice coil motor (VCM). Specifically, electrical current passed through a coil of the VCM applies a torque to the rotary actuator, so that the read head can seek and follow desired data tracks on the spinning disk.
However, the industry trend towards increasing areal data density has necessitated substantial reduction in the spacing between data tracks on the disk. Also, disk drive performance requirements, especially requirements pertaining to the time required to access desired data, have not allowed the rotational speed of the disk to be reduced. In fact, for many disk drive applications, the rotational speed has been significantly increased. A consequence of these trends is that increased bandwidth is required for servo control of the read head position relative to data tracks on the spinning disk.
One solution that has been proposed in the art to increase disk drive servo bandwidth is dual-stage actuation. Under the dual-stage actuation concept, the rotary actuator that is driven by the VCM is employed as a coarse actuator (for large adjustments in the HSA position relative to the disk), while a so-called “microactuator” having higher bandwidth but lesser stroke is used as a fine actuator (for smaller adjustments in the read head position). Various microactuator designs have been proposed in the art for the purpose of dual-stage actuation in disk drive applications. Some of these designs utilize one or more piezoelectric microactuators that are affixed to a component of the suspension assembly. For example, the piezoelectric microactuator may be affixed to the mounting plate or an extension thereof, and/or the load beam or an extension thereof, or to the flexure tongue (a.k.a. the “gimbal tongue”) to which the read head is bonded.
However, generally, the further the microactuator is disposed from the read head on the suspension assembly, the less bandwidth it can provide. This is due to the dynamics introduced by the intermediate structure of the suspension assembly. On the other hand, the closer the microactuator is disposed to the read head on the suspension assembly, the lesser stroke it can typically provide. As track density increases, the need for additional bandwidth tends to exceed the need for additional stroke, tending to favor microactuator designs that are more distally located (e.g., at or near the read head). Hence there is a need in the information storage device arts for a distally located microactuator design that can provide both adequate stroke and adequate bandwidth for fine actuation.
Moreover, certain prior art design concepts in which the microactuator is disposed on the flexure tongue may have other performance disadvantages. For example, in certain designs, the motion imparted by the microacutator may be undesirably coupled with the yaw or “sway” mode of vibration of the head gimbal assembly. Also for example, the microactuator operation may require relative motion at the dimple contact location between the flexure tongue and the load beam, which can cause undesirable fretting, debris, and a stick-slip motion characteristic. Also for example, the flexure design for accommodating the microactuator may lack desired stiffness in certain directions (e.g., vertical stiffness or yaw stiffness), and/or may lack desired compliance in other directions (pitch compliance or roll compliance). Also for example, the microactuated HGA design may include additional parts and complexity that add cost and time to the manufacturing process, such as where the structure that supports the microactuator components is attached to (rather than built into and integral with) the flexure tongue. Also for example, the flexure design for accommodating a microactuator on the tongue may not provide for adequate bonding area to reliably bond the head to the tongue with consistently adequate strength in a practical high volume manufacturing process.
Hence, there is a need in the information storage device arts for improved fine actuator (“microactuator”) designs for HGAs.